Conceal an entrance by means of superscatterer

By using the novel property of the rectangular superscatterer, we propose a design which can conceal an entrance from electromagnetic wave detection. Such a superscatterer is realized by coating a negative index material shell on a perfect electrical conductor rectangle cylinder. The results are numerically confirmed by full-wave simulations both in the far-field and near-field.Comment: 10 pages, 4 figure

Firing Control Optimization of Impulse Thrusters for Trajectory Correction Projectiles

This paper presents an optimum control scheme of firing time and firing phase angle by taking impact point deviation as optimum objective function which takes account of the difference of longitudinal and horizontal correction efficiency, firing delay, roll rate, flight stability, and so forth. Simulations indicate that this control scheme can assure lateral impulse thrusters are activated at time and phase angle when the correction efficiency is higher. Further simulations show that the impact point dispersion is mainly influenced by the total impulse deployed, and the impulse, number, and firing interval need to be optimized to reduce the impact point dispersion of rockets. Live firing experiments with two trajectory correction rockets indicate that the firing control scheme works effectively

Research on prevention and control methods of land subsidence induced by groundwater overexploitation based on three-dimensional fluid solid coupling model—a case study of Guangrao County

Land subsidence is an environmental geological phenomenon with slowly decreasing ground elevation, The North China Plain is one of the areas with the most serious land subsidence in China, and Guangrao County is one of the subsidence centers. This paper is based on the hydrogeological and engineering geological data of Guangrao County, the groundwater monitoring data for many years and the land subsidence monitoring data, systematically analyzes the dynamic characteristics of groundwater, the distribution and evolution of land subsidence, and the correlation between groundwater exploitation and land subsidence development in different layers of this area. Based on Biot porous medium consolidation theory, establishes a three-dimensional fluid solid coupling numerical model of land subsidence in Guangrao County, restores the development process of land subsidence, predicts and analyzes the subsidence evolution law under different groundwater exploitation schemes, and proposes targeted prevention and control measures. The research results show that: the shallow groundwater forms a cone of depression with Guangbei Salt Field as the center, and the deep groundwater forms an elliptical regional cone of depression with the urban area as the center. The ground is gradually formed two small settlement areas with the urban area of Guangrao County and Guangbei Salt Field as the settlement center, and there is a trend of interrelated expansion. The three-dimensional fluid solid coupling model of land subsidence accurately restored the development process of land subsidence in the study area, predicted that under the current groundwater exploitation conditions, by 2040, the settlement of Guangrao urban settlement center will increase to 1,350 mm, forming a large regional funnel centered around the urban area, and gradually developing and expanding around. Prohibition of groundwater exploitation in the main funnel area is a more reasonable and effective exploitation plan to prevent the development of land subsidence

Comprehensive Evaluation of Self-Healing Polyampholyte Gel Particles for the Severe Leakoff Control of Drilling Fluids

Lost circulation has been a serious problem to be solved in many drilling practices during oil, gas and geothermal well drillings. Many materials have been developed and evaluated for the purpose. However, their performance to plug severe leakoff is very limited. Herein, an injectable self-healing hydrogel based on polyampholyte with sulfonated and quaternary ammonium functionalities (P(MPTC-co-NaSS)) was developed and comprehensively evaluated to prevent the severe loss of fluids to formation. By incorporating cation-π (π is for aromatic residues) interaction, the hydrogel shown self-healing property and robustness in severe environment (temperature, salt) by comparison with other hydrogels merely consisting of cation-anion and H-bonding interactions. Aromatic residues enhanced thermal stability above 310 °C. The plugging measurement shown that an addition of 2 wt% dried gel particles can plug high-permeability formation and endure a high pressure of 6 MPa, produce much lower circulation loss and result in a dramatically increased loss volume reduction rate (63.5%) compared with a commercial polymer gel product and an inert material (9.4%) after a self-healing process. Markedly, P(MPTC-co-NaSS) can be used in a wide range of formation temperature (as high as 150 °C) and salt concentrations (NaCl, CaCl2, as high as 15 wt %). In addition to suitable particle size and mechanically robustness, it was also attributed to the soft, swelling, deformable, toughness and self-healable features of P(MPTC-co-NaSS) gel particles as well as the strong adhesion to negatively charged formations in water, even under high thermal and saline condition. These characteristics also contributed to a long-term plugging performance, beneficial to avoid repeated lost circulation in drilling operation. Besides, this self-healing polyampholyte gel particles dispersed well in saline fluid and maintained stable rheological properties after hot rolling, which was favorable to drilling fluid circulation. This study shown the application potential of self-healing materials as plugging material candidate in petroleum drilling industry

A Magnetically and Thermally Controlled Liquid Metal Variable Stiffness Material

Smart materials that can actively tune their stiffness are of great interest to many fields, including the construction industry, medical devices, industrial machines, and soft robotics. However, developing a material that can offer a large range of stiffness change and rapid tuning remains a challenge. Herein, a liquid metal variable stiffness material (LMVSM) that can actively and rapidly tune its stiffness by applying an external magnetic field or by changing the temperature is developed. The LMVSM is composed of three layers: a gallium–iron magnetorheological fluid (Ga–Fe MRF) layer for providing variable stiffness, a nickel–chromium wire layer for Joule heating, and a soft heat dissipation layer for accelerating heating and rapid cooling. The stiffness can be rapidly increased by 4 times upon the application of a magnetic field or 10 times by solidifying the Ga–Fe MRF. Finally, the LMVSM is attached to a pneumatically controlled soft robotic gripper to actively tune its load capacity, demonstrating its potential to be further developed into smart components that can be widely adopted by smart devices